Currently it's hardcoded. You can see it in this line in backend_pdf.py:
https://github.com/matplotlib/matplotlib/blob/9ca2c4118f684b4e145bd109008f77731d2d7cd4/lib/matplotlib/backends/backend_pdf.py#L1061
You could change that line.
However, long term, I think we need to add a hatch_line_width kwarg to
artists -- and perhaps further (though this would break backward
compatibility) separate out the edge color from the hatch line color, so
one could have (for example) a black rectangle filled with red hatching
(not currently possible without layering objects).
Cheers,
Mike
On 04/25/2011 04:21 PM, T J wrote:
> On Mon, Apr 25, 2011 at 1:15 PM, T J<tjhnson@...> wrote:
>> I am using the PDF backend and specifying a hatch for a fill_between()
>> call. The resultant PDF looks okay, but the hatch lines are too
>> light.
>>
>> Is there a way to darken them? Also, is it possible to change the
>> color of the hatch lines? I'm okay solutions that are low-level hacks.
>> I just need the PDF to have proper hatches.
>>
> I can change their color by specifying 'edgecolor' to PathPatch, but
> their intensity is still too low. :(
>
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On Mon, Apr 25, 2011 at 1:15 PM, T J <tjhnson@...> wrote:
> I am using the PDF backend and specifying a hatch for a fill_between()
> call. The resultant PDF looks okay, but the hatch lines are too
> light.
>
> Is there a way to darken them? Also, is it possible to change the
> color of the hatch lines? I'm okay solutions that are low-level hacks.
> I just need the PDF to have proper hatches.
>
I can change their color by specifying 'edgecolor' to PathPatch, but
their intensity is still too low. :(

I am using the PDF backend and specifying a hatch for a fill_between()
call. The resultant PDF looks okay, but the hatch lines are too
light.
Is there a way to darken them? Also, is it possible to change the
color of the hatch lines? I'm okay solutions that are low-level hacks.
I just need the PDF to have proper hatches.